Chorionic Villus Sampling and Amniocentesis
Chorionic Villus Sampling and Amniocentesis
Chorionic villus sampling (CVS) and amniocentesis are diagnostic tests that can be undertaken during pregnancy. These tests will be offered to you under the following circumstances:
- If you have an higher chance result for Down’s syndrome, Edwards’ syndrome or Patau’s syndrome
- If you are at higher chance of passing on an inherited condition to your baby, for example cystic fibrosis, sickle cell disease or thalassemia major
- If you had a previous pregnancy where your baby had a genetic or chromosomal abnormality
- If a significant fetal abnormality is seen on scan
- If there are any other clinical indications
- Performed from 11+ weeks in pregnancy
- Sample of placenta is taken
- 1% risk of procedure related miscarriage ay this hospital (national risk 1-2%)
- Performed from 16 weeks in pregnancy
- Sample of amniotic fluid is taken
- 0.5% risk of procedure related miscarriage at this hospital (national risk 1%)
The doctor will discuss the test prior to starting the procedure and perform a scan to check that it is clinically appropriate to proceed. Both tests take approximately 3-4 minutes, although your whole appointment will last 20-30 minutes. During the procedure, under ultrasound guidance, a needle is passed through your abdomen into your uterus and a sample is taken.
If your blood group is rhesus negative you may require an injection of Anti-D following either of these procedures.
After the procedure it is recommended that you rest for the remainder of the day. You may experience some abdominal discomfort; it is safe to use Paracetamol in these circumstances.
The sample is sent to the laboratory where it will undergo a rapid test (QF-PCR) which checks for the three most common chromosomal abnormalities, Down’s syndrome, Edwards’ syndrome and Patau’s syndrome. In specific clinical circumstances this test will also check for Turner syndrome. The result is usually available within 4 working days; once we receive the information we will contact you by telephone and plan your ongoing care.
If you have a higher chance screening result or request a diagnostic test without clinical indication, only a QF-PCR test will be performed on the sample.
CVS and amniocentesis do not detect structural abnormalities and therefore we recommend a scan between 18 and 21 weeks of pregnancy, irrespective of the results of the diagnostic test.
In certain clinical circumstances further testing will be undertaken on the sample. This will be discussed with you before the procedure.
| Test | Indication | Method | Timeframe |
|---|---|---|---|
| DNA Analysis | Known risk of specific genetic disorder | DNA from fetal cells is examined to find out whether the baby has the known genetic disorder. The type of test will depend on the specific disorder. | Dependant on specific test |
| Full karyotype | Abnormal rapid test result / other indication | Looks at all 23 pairs of chromosomes under a microscope. This test can see if there are any extra or missing whole chromosomes, translocations and large segment imbalances. This test will not detect gene mutations and may not detect small segment imbalances or mosaicism. | 10-21 days |
| Array CGH | Significant fetal abnormality on ultrasound | Screens all 23 pairs of chromosomes and can detect very small changes which can be gains and/or losses of chromosome material that cannot be seen under a microscope. This test will not detect balanced chromosome rearrangements and gene mutations and may not detect some very small imbalances or mosaicism. | 10-21 days |
All results will be communicated and discussed with you as soon as they are received and where appropriate follow up will be arranged. In some circumstances it may be necessary to take parental blood samples to help interpret the results. If this is the case you will be informed and asked to attend for a blood test as soon as possible.
If you have any questions or concerns, please contact the specialist midwives at:
- Chelsea and Westminster on 0203 315 5874
- West Middlesex on 020 8321 6727/5016
If you have a medical concern outside office hours please contact the maternity help line at:
- Chelsea and Westminster on 0203 315 6000
- West Middlesex on 0208 321 5839
Or attend your local accident and emergency department
For further information:
Screening in pregnancy: information leaflets - GOV.UK (www.gov.uk)